The IEEE 802.11 family of specifications provides a method for wireless transmission of data between devices. The spectrum assignments in which IEEE 802.11 wireless networks can be used are a finite resource that is getting more congested as IEEE 802.11 becomes more popular.
The IEEE 802.11 standard is not well suited to the situation where two (or more) unrelated networks are within radio range of each other and use the same radio frequency (RF) channel. Two or more networks operating on the same RF channel within radio range of each other increases the probability of packet collisions.
One technique that has been suggested within the IEEE 802.11 standard to improve quality of service (QoS) is based on prioritising traffic, i.e. giving one of the networks prioritised access to the wireless medium.
IEEE 802.11 provides three channel access methods for providing QoS prioritised traffic.
The first method (called Enhanced Distributed Channel Access (EDCA)) modifies the time a station or access point waits between sensing that the wireless medium is not busy and starting to transmit. The waiting time is modified in such a way to make higher priority traffic more likely to be the first to be transmitted.
The second channel access method (called Point Coordination Function (PCF)) is based on an access point providing stations with contention free periods (CFP) in a period immediately following the transmission of a beacon frame from the access point. A polling mechanism is used where an access point grants a transmission opportunity to a station. All other stations remain silent during a CFP.
The third channel access method (called Hybrid Coordination Function Controlled Channel Access (HCCA)) is based on an access point providing stations with contention free periods. A polling mechanism is used where an access point grants a transmission opportunity to a station. All other stations remain silent during a CFP.
U.S. patent application Ser. No. 10/411,173 (published as US 2003/0202498) describes an access point for a wireless local area network. The access point is arranged to service its stations by using a Point Coordination Function (PCF) protocol and to monitor overlap with neighbouring access points. To mitigate overlap, the access point and overlapping neighbouring access points synchronise in such a way that the access point can service its stations in an overlap areas during a certain servicing time, while the overlapping neighbouring access points are silent, and vice versa. A silence trade-off mechanism is used to assure that overlapping access points get their fair share of available bandwidth.
The following document may be relevant to understanding the present invention: IEEE Std 802.11, 2007 Edition—Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications.